Electrical devices

ABSTRACT

An electrical device which comprises first and second laminar electrodes and a laminar PTC resistive element sandwiched between them, the device comprising  
     (a) a main portion which comprises a main part of the first electrode, a main part of the second electrode, and a main part of the resistive element; and  
     (b) a first connection leg which extends away from the main portion and which comprises a first leg part of the first electrode which is integral with the main part of the first electrode, and a first leg part of the resistive element which is integral with the main part of the resistive element.  
     Such devices can be secured to circuit boards in a variety of ways, and to elastically deformed terminals. Preferably preferred devices contain two laminar electrodes, with a PTC element between them, and a cross-conductor which passes through the thickness of the device and contacts one only of the two electrodes. The cross-conductor permits connection to both electrodes from the same side of the device, and also makes it possible to carry out the steps for preparing such devices on an assembly which corresponds to a number of individual devices, with division of the assembly as the final step.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of (1) copending,commonly assigned U.S. patent application Ser. No. 08/152,070, filedNov. 12, 1993, by Graves, Zhang, Chandler, Chan and Fang (Docket No.MP1454-US2) which is a file wrapper continuation of U.S. patentapplication Ser. No. 07/910,950, filed Jul. 9, 1992 (Docket No.MP1454-US1), now abandoned, and (2) copending, commonly assigned U.S.patent application Ser. No. 08/121,717, filed Sep. 15, 1993, by Fang,Siden, Thompson and Zhang (Docket No. MP1490-US1), the disclosures ofwhich are incorporated herein by reference for all purposes.

[0002] This application is also related to copending InternationalApplication No. PCT/US 93/06480, filed Jul. 8, 1993, by RaychemCorporation (Docket No. MP1454-PCT) which claims priority from U.S.patent application Ser. No. 07,910,950, to copending, commonly assignedU.S. patent application Ser. No. 08/242,916, filed May 16, 1994, byZhang and Fang (Docket No. MP1509-US1), and to copending, commonlyassigned U.S. patent application Ser. No. 08/257,586, filed Jun. 9,1994, by Zhang, Thompson, Toth and Beadling (Docket No. MP1515-US1). Theentire disclosure of each of those U.S. and International patentapplications is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] This invention relates to electrical devices.

[0005] 2. Introduction to the Invention

[0006] Many electrical devices comprise two laminar electrodes and,sandwiched between them, an electrical element which may be a conductor,e.g. a resistive element, as for example in a resistor or a varistor, ora non-conductor, as for example in a capacitor. Particularly usefuldevices of this type are circuit protection devices which comprise alaminate of two laminar electrodes and, sandwiched between theelectrodes, a laminar resistive element which exhibits PTC behavior. Theresistive element may be composed of conductive polymer (this term beingused to denote a composition comprising a polymer and, dispersed, orotherwise distributed, therein, a particulate conductive filler) or aceramic, e.g. a doped barium titanate. When a conductive polymer isused, such devices are generally prepared by stamping (or otherwisecutting) a plurality of the devices out of a laminate of a sheet of theconductive polymer between two metal foils. When a ceramic is used, suchdevices are usually prepared by applying liquid electrode material tothe major surfaces of a preformed laminar resistive element, andsolidifying the liquid electrode material.

[0007] The products of such processes can sometimes be used without theaddition of electrical leads, for example by installation between twospring-loaded terminals. In most cases, however, an electrical lead mustbe secured to each of the laminar electrodes, so that the device can beconnected to other components of a circuit, e.g. mounted on a circuitboard. The addition of leads is an additional expense and usuallyinvolves heating (e.g. during soldering or welding) which can causedamage, particularly to conductive polymer elements. The latter problemis particularly severe when a conductive polymer is heated a second timewhen the leads are connected to other circuit elements, in particularwhen the leads are connected to a printed circuit board by a solderingprocess. A further problem which can arise when such devices are to bemounted on a printed circuit board is that they protrude further fromthe board than is desirable.

SUMMARY OF THE INVENTION

[0008] We have now realized, in accordance with the present invention,that when at least one of the laminar electrodes of an electrical deviceas described above is to be connected to an electrical conductor on aninsulating substrate, in particular a printed circuit board, then byappropriate modification of the device and/or of the configuration ofthe electrical conductor on the substrate, the connection can be madeeither without the need for a lead (or other connecting member), or withthe aid of a connecting member which is electrically connected to theelectrode in the same step as it is electrically connected to theconductor on the substrate. We have also realized, in accordance withthe present invention, that such modification can also be extremelyvaluable for electrical devices which are connected via elasticallydeformed terminals. The invention will be described herein chiefly byreference by circuit protection devices comprising a laminar PTCresistive element sandwiched between, and preferably contacted directlyby, two laminar electrodes, but it is also applicable to other devicescomprising two laminar electrodes and another type of laminar elementsandwiched between them.

[0009] Typically, the devices of the invention have, in addition to amain portion having a normal configuration (typically a simple geometricshape such as a rectangle or a circle), at least one connection legwhich extends away from the main portion and which comprises anextension of the PTC resistive element and an extension of one of theelectrodes secured to the PTC element. The connection leg can, butpreferably does not, also contain an extension of the other electrode.

[0010] In one use of such modified devices, the device is mounted on acircuit board by inserting the end of the connection leg into anaperture in the board and soldering the electrode to a metal conductorwhich is secured to the board and which leads to the aperture. If theconnection leg does not include extensions of both electrodes, then thesolder connection can be carried out in conventional ways. If the legdoes include extensions of both electrodes in the region of theaperture, then care must be taken to ensure that the solder connectsonly the desired electrode to the metal conductor. For this purpose, themetal conductor can lead to one side only of the aperture and preferablycan be substantially narrower than the aperture and the face of theconnection leg to which it is soldered. A circuit board having a metalconductor and an aperture of this kind is believed to be novel per seand as such forms a part of the present invention. Generally, a devicewhich is to be mounted in this way will be modified so that it has twoconnection legs of the kind described, extending in the same directionfrom the main portion of the device, so that the legs can be mounted inadjacent aperture in the same circuit board. The legs preferably havedistal portions which are inserted into the apertures in the board, andintermediate stand-off portions which cannot pass through the aperturesand which ensure that the main part of the device is spaced apart fromthe board.

[0011] As discussed above (and in greater detail below), when the deviceis to be mounted in apertures in a circuit board, the connection leg cancomprise extensions of both electrodes; preferably, however, theconnection leg includes a bridge portion which extends across the fullwidth of the leg and which includes only one of the electrodes so thatthe device can be soldered to a conventional circuit board in theconventional way. When the connection leg is of the latter kind, thedevice can be mounted in the apertures of a circuit board as outlinedabove, or can be mounted flat on top of a circuit board.

[0012] To mount the device flat on top of a circuit board, the device isplaced on the substrate with the electrode which extends into theconnection leg on top. The bottom electrode is connected directly to aconductor on the board. The top electrode is connected to anotherconductor on the board by means of a connection member secured to thetop electrode and extending downwards below the lower face of the PTC(or other) element. In a particularly preferred embodiment, theconnection member is a transverse conductive member which passes throughthe PTC (or other) element; such a transverse member is often referredto herein as a “cross-conductor”. The connection member is preferablyelectrically connected to the upper electrode before it is electricallyconnected to the conductor on the board; alternatively, both electricalconnections can be made simultaneously. If there are two connectionlegs, one containing an extension of one of the electrodes only, and theother containing an extension of the other of the electrodes only, thedevice can be placed on the board with either electrode on top, and ifthe device is symmetrical, the connections to the device and thesubsequent operation of the device can be the same.

[0013] The novel devices of the invention can be made by securingelectrodes of appropriate shapes to resistive elements of the desiredfinal shape; or by securing electrode precursors of appropriate shapesto resistive elements which are larger than the desired final shape, andthen dividing the assembly into a plurality of devices of the desiredfinal shape or shapes; or by preparing a plurality of devices of thedesired final shape or shapes by division of a simple laminate ofconstant cross-section and, if desired or necessary, and before or afterthe division, removing unwanted portions of one or both of theelectrodes. Such removal can be effected for example by milling or byetching. Preferably such removal of unwanted portions of the electrodesremoves little or none of the PTC resistive element, which providesdesirable physical strength to the connection leg. Preferably also,when, as is preferred, the connection leg includes an extension of onlyone of the electrodes, the leg does also include a residual portion ofthe second electrode. The residual portion is not electrically connectedto the main portion, but provides valuable physical properties,including strength and resistance to deformation when connection to thefirst electrode is made by a spring clip or other elastically deformedterminal. A preferred process for preparing devices of the invention isdescribed in copending, commonly assigned U.S. patent application Ser.No. 08/257,586 (Docket No. MP1515-US1), incorporated by referenceherein.

[0014] The devices of the invention which contain at least one crossconductor which passes though the resistive element can be made byprocesses in which the various operative steps are carried out on anassembly which corresponds to a plurality of devices in both thelongitudinal and the lateral dimension, and which, as the final step ofthe process, is divided into a plurality of devices. The ability toprepare devices in this way becomes increasingly important as the size(and, therefore, resistance) of the device deceases and this inventionis especially valuable for preparing devices which are to be mounted oncircuit boards and in other situations in which the smaller the size andstance of the device, the better. For example, such a process can beused to make circuit protection devices having a surface area of about0.02 inch² (13 mm²) or even less.

[0015] The various steps of the process are preferable carried out at atemperature substantially below the melting point of the PTC element, inorder to minimize changes in its electrical properties.

[0016] In one preferred aspect, this invention provides a novel assemblywhich comprises

[0017] (1) a PTC resistive element which

[0018] (a) is composed of a resistive material which exhibits PTCbehavior,

[0019] (b) has a first face and a second face, and

[0020] (c) defines an aperture which runs between the first and secondfaces;

[0021] (2) a transverse conductive member which

[0022] (a) lies within the aperture defined by the PTC element,

[0023] (b) runs between the first and second faces of the PTC element,and

[0024] (c) is secured to the PTC element; and

[0025] (3) a first laminar conductive member which (a) is secured to thefirst face of the PTC element and (b) is physically and electricallyconnected to the transverse conductive member.

[0026] This novel assembly can be

[0027] (i) an electrical device which is ready for connection (the firstlaminar conductive member then providing the first electrode, and thedevice including also a second electrode which is not electricallyconnected to the cross-conductor), or

[0028] (ii) a structure which (if necessary after further processing)can be divided into a plurality of electrical devices, each of thedevices containing at least one cross-conductor.

[0029] In another preferred aspect, this invention provides anelectrical assembly which comprises

[0030] (A) a printed circuit board including first and second conductivetraces on a surface thereof, and

[0031] (B) an electrical device which comprises

[0032] (1) a laminar PTC resistive element which

[0033] (a) is composed of a resistive material which exhibits PTCbehavior, and

[0034] (b) has a first face and a second face;

[0035] (2) a first laminar electrode which is secured to the first faceof the PTC element;

[0036] (3) a second laminar electrode which is secured to the secondface of the PTC element;

[0037] (4) an additional laminar conductive member which (a) is securedto the second face of the PTC element and (b) is spaced apart from thesecond electrode;

[0038] the PTC element, the first electrode and the additional laminarconductive member defining an aperture which runs between the firstelectrode and the additional conductive member, through the PTC element;and

[0039] (5) a transverse conductive member which

[0040] (a) lies within the aperture, and

[0041] (b) is physically and electrically connected to the firstelectrode and the additional conductive member;

[0042] said electrical device being placed on the printed circuit boardand parallel thereto, with the first conductive trace physically andelectrically connected to the additional conductive member, and thesecond conductive trace physically and electrically connected to thesecond electrode.

[0043] In another preferred aspect, this invention provides a method ofmaking electrical devices which comprises

[0044] (A) providing an assembly which corresponds to a plurality of theelectrical devices and which comprises

[0045] (1) a laminar PTC resistive element which (i) is composed of aresistive material exhibiting PTC behavior, and (ii) has a first faceand a second face,

[0046] (2) a first laminar conductive member which is secured to thefirst face of the PTC element, and

[0047] (3) a second laminar conductive member which is secured to thesecond face of the PTC element;

[0048] (B) making a plurality of apertures through the thickness of theassembly provided in step (A), the apertures being arranged in a regularpattern;

[0049] (C) simultaneously with step (B), or after step (B), placing aplurality of transverse conductive members within the apertures, inelectrical contact with the first laminar conductive member;

[0050] (D) removing predetermined portions of at least one of the firstand second conductive members; and

[0051] (E) after steps (A) to (D), dividing the assembly into aplurality of electrical devices, each device comprising

[0052] (1) a part of the PTC resistive element,

[0053] (2) a part of the first laminar conductive member, said partproviding a first electrode,

[0054] (3) a part of the second laminar conductive member, said partproviding a second electrode,

[0055] (4) a residual part of the second laminar conductive member, and

[0056] (5) at least one transverse conductive member which electricallyconnects the residual part and the first electrode.

[0057] In this method, step (D) can be carried out before or after step(B) or before or after step (C).

[0058] When the PTC material is a conductive polymer, this methodpreferably makes use of a novel assembly which forms part of the presentinvention, namely an assembly which comprises

[0059] (1) a laminar PTC resistive element which (i) is composed of aconductive polymer exhibiting PTC behavior, and (ii) has a first faceand a second face,

[0060] (2) a first laminar conductive member which is secured to thefirst face of the PTC element, and

[0061] (3) a second laminar conductive member which is secured to thesecond face of the PTC element;

[0062] the PTC element and the first and second laminar conductivemembers defining a plurality of apertures which pass through thethickness of the assembly, and the apertures being arranged in a regularpattern.

[0063] In this assembly, preferably

[0064] (a) the apertures are arranged in a plurality of straight lines,and

[0065] (b) the first laminar conductive member is in the form of aplurality of strips which are parallel to each other and to the lines ofapertures.

[0066] It is particularly preferred that

[0067] (a) each strip of the first conductive member contains twoadjacent lines of aperture, and

[0068] (b) the second laminar conductive member is also in the form of aplurality of strips which are parallel to each other and to the lines ofapertures with each strip containing two adjacent lines of apertures,one of said lines of apertures falling within a first strip of the firstconductive member and the other line of apertures falling within asecond strip of the first conductive member.

BRIEF DESCRIPTION OF THE DRAWING

[0069] The invention is illustrated in the accompanying drawings, inwhich

[0070]FIGS. 1 and 2 are plan and cross sectional views of a device ofthe invention containing a cross-conductor;

[0071]FIGS. 3 and 4 are cross sectional views of devices of theinvention containing a cross-conductor;

[0072]FIGS. 5 and 6 are plan and cross sectional views of a device ofthe invention containing a cross-conductor and mounted on a printedcircuit board parallel to the board;

[0073]FIGS. 7 and 8 are plan and cross sectional views of part of anassembly of the invention which can be divided into a plurality ofindividual devices of the invention containing a cross-conductor;

[0074]FIG. 9 shows a plan view of another electrical assembly of theinvention showing an electrical device of the invention mounted in theapertures of a circuit board and at right angles to the board;

[0075]FIG. 10 is a cross-sectional view of an assembly of the inventionalong line 2-2 of FIG. 9;

[0076]FIG. 11 is a plan view of another electrical assembly of theinvention showing an electrical device of the invention mounted in theapertures of a circuit board and at right angles to the board;

[0077]FIG. 12 is a cross-sectional view of an assembly of the inventionalong line 4-4 of FIG. 11;

[0078]FIG. 13 is a bottom view of the assembly of FIG. 11;

[0079]FIG. 14 is a top view of another assembly of the invention whichincludes an electrical device of the invention mounted on a circuitboard and parallel thereto; and

[0080]FIG. 15 is a cross-sectional view through the thickness of theassembly of FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

[0081] All embodiments and aspects of the invention set out below are tobe regarded as part of Applicants' invention, even where the followingdetailed description is broader than the summary of the invention setout above. Conversely, the following detailed description should not beregarded as in any way limiting the generality of the summary of theinvention set out above.

[0082] As described and claimed below, and as illustrated in theaccompanying drawings, the present invention can make use of a number ofparticular features. Where such feature is disclosed in a particularcontext or as part of a particular combination, it can also be used inother contexts and in other combinations, including for example othercombinations of two or more such features.

[0083] PTC Compositions

[0084] The PTC compositions used in the present invention are preferablyconductive polymers which comprise a crystalline polymer component and,dispersed in the polymer component, a particulate filler component whichcomprises a conductive filler, e.g. carbon black or a metal. The fillercomponent may also contain a non-conductive filler, which changes notonly the electrical properties of the conductive polymer but also itsphysical properties. The composition can also contain one or more othercomponents, e.g. an antioxidant, crosslinking agent, coupling agent orelastomer. For use in circuit protection devices, the PTC compositionpreferably has a resistivity at 23° C. of less than 50 ohm-cm,particularly less than 10 ohm-cm, especially less than 5 ohm-cm.Suitable conductive polymers for use in this invention are disclosed forexample in U.S. Pat. No. 4,237,441 (van Konynenburg et al), U.S. Pat.No. 4,304,987 (van Konynenburg), U.S. Pat. No. 4,388,607 (Toy et al),U.S. Pat. No. 4,514,620 (Cheng et al), U.S. Pat. No. 4,534,889 (vanKonynenburg et al), U.S. Pat. No. 4,545,926 (Fouts et al), U.S. Pat. No.4,560,498 (Horsma et al), U.S. Pat. No. 4,591,700 (Sopory), U.S. Pat.No. 4,724,417 (Au et al), U.S. Pat. No. 4,774,024 (Deep et al), U.S.Pat. No. 4,935,156 (van Konynenburg), and U.S. Pat. No. 5,049,850 (Evanset al), and copending, commonly assigned U.S. patent application Ser.No. 07/893,626 (Chandler et al. filed Jun. 5, 1992). The disclosure ofeach of these patents and applications is incorporated herein byreference.

[0085] The PTC resistive element is preferably a laminar element, andcan be composed of one or more conductive polymer members, at least oneof which is composed of a PTC material. When there is more than oneconductive polymer member, the current preferably flows sequentiallythrough the different compositions, as for example when each compositionis in the form of a layer which extends across the whole device. Whenthere is a single PTC composition, and the desired thickness of the PTCelement is greater than tat which can conveniently be prepared in asingle step, a PTC element of the desired thickness can conveniently beprepared by joining together, eg. laminating by means of heat andpressure, two or more layers, eg. melt-extruded layers, of the PTCcomposition. When there is more than one PTC composition, the PTCelement will usually be prepared by joining together, eg. laminating bymeans of heat and pressure, elements of the different compositions. Forexample, a PTC element can comprise two laminar elements composed of afirst PTC composition and, sandwiched between them, a laminar elementcomposed of a second PTC composition having a higher resistivity thanthe first.

[0086] When a PTC device is tripped, most of the voltage dropped overthe device is normally dropped over a relatively small part of thedevice which is referred to as the hot line, hot plane or hot zone. Inthe devices of the invention, the PTC element can have one or morefeatures which help the hot line to form at a desired location, usuallyspaced apart from both electrodes. Suitable features of this kind foruse in the present invention are disclosed for example in U.S. Pat. Nos.4,317,027 and 4,352,083 (Middleman et al), U.S. Pat. Nos. 4,907,340 and4,924,072 (Fang et al), the disclosures of which are incorporated hereinby reference.

[0087] Laminar Electrodes

[0088] Particularly useful devices of the invention comprise two metalfoil electrodes, and a PTC conductive polymer element sandwiched betweenthem, especially such devices which are used as circuit protectiondevices and have low resistance at 23° C., generally less than 50 ohm,preferably less than 15 ohm, more preferably less than 10 ohm,particularly less than 5 ohm, especially less than 3 ohm, with yet lowerresistance being possible, e.g. less than 1 ohm, even less than 0.5 ohm.Particularly suitable foil electrodes are microrough metal foilelectrodes, including in particular electrodeposited nickel foils andnickel-plated electrodeposited copper foil electrodes, in particular asdisclosed in U.S. Pat. No. 4,689,475 (Matthieson) and U.S. Pat. No.4,800,253 (Kleiner et al), the disclosure of each of which isincorporated herein by reference. A variety of laminar deices which canbe modified in accordance with the present invention are disclosed inU.S. Pat. No. 4,238,812 (Middleman et al), U.S. Pat. No. 4,255,798(Simon), U.S. Pat. No. 4,272,471 (Walker), U.S. Pat. No. 4,315,237(Middleman et al), U.S. Pat. No. 4,317,027 (Middleman et al), U.S. Pat.No. 4,330,703 (Horsma et al), U.S. Pat. No. 4,426,633 (Taylor), U.S.Pat. No. 4,475,138 (Middleman et al), U.S. Pat. No. 4,724,417 (Au etal), U.S. Pat. No. 4,780,598 (Fahey et al), U.S. Pat. No. 4,845,838(Jacobs et al), U.S. Pat. No. 4,907,340 (Fang et al), and U.S. Pat. No.4,924,074 (Fang et al), the disclosure of each of which is incorporatedherein by reference. The electrodes can be modified so as to producedesired thermal effects.

[0089] The electrodes are preferably secured directly to the PTCresistive element.

DETAILED DESCRIPTION OF THE DEVICES, ASSEMBLIES AND METHODS OF THEINVENTION IN WHICH A CROSS-CONDUCTOR IS EMPLOYED Apertures andCross-Conductors

[0090] The term “aperture” when used herein in connection with a deviceof the invention or an assembly to be converted into a plurality ofdevices of the invention (but not when used herein in connection withthe apertures in a circuit board), denotes an opening which

[0091] (a) has a closed cross section, e.g. a circle, an oval, or agenerally rectangular shape, or

[0092] (b) has an open reentrant cross section which (i) has a depth atleast 0.15 times, preferably at least 0.5 times, particularly at least1.2 times, the maximum width of the cross section, e.g. a quarter circleor a half circle or an open-ended slot, and/or (ii) has at least onepart where the opposite edges of the cross section are parallel to eachother.

[0093] In assemblies of the invention which can be divided into aplurality of electrical devices, the apertures will normally be ofclosed cross section, but if one or more of the lines of division passesthrough an aperture of closed cross section, then the apertures in theresulting devices will then have open cross sections. It is importantthat any such open cross section is a reentrant cross section as definedabove, in order to ensure that the cross-conductor is not damaged ordislodged during installation or use of the device.

[0094] The aperture can be a circular hole, and for many purposes thisis satisfactory in both individual devices and assemblies of devices.However, if the assembly includes apertures which are traversed by atleast one line of division, elongate apertures may be preferred becausethey require less accuracy in the lines of division.

[0095] When the aperture is not traversed by a line of division, it canbe as small as is convenient for a cross-conductor having the necessarycurrent-carrying capacity. For circuit protection devices, holes ofdiameter 0.1 to 5 mm, preferably 0.15 to 1.0 mm, e.g. 0.2 to 0.5 mm, aregenerally satisfactory. Generally a single cross-conductor is all thatis needed to make an electrical connection to the first electrode fromthe opposite side of the device. However, two or more cross-conductorscan be used to make the same connection. The number and size of thecross-conductors, and, therefore, their thermal capacity, can have anappreciable influence on the rate at which a circuit protection devicewill trip.

[0096] The aperture can be formed before the cross-conductor is put inplace, or the formation of the aperture and the placing of thecross-conductor can be carried out simultaneously. A preferred procedureis to form the aperture, e.g. by drilling, slicing or any otherappropriate technique, and then to plate or otherwise coat or fill theinterior surface of the aperture. The plating can be effected byelectroless plating, or electrolytic plating, or by a combination ofboth. The plating can be a single layer or multiple layers, and can becomposed of a single metal or a mixture of metals, in particular asolder. The plating will often also be formed on other exposedconductive surfaces of the assembly. If such plating is not desired,then the other exposed conductive surfaces must be masked or otherwisedesensitized. Generally, however, the plating is carried out at a stageof the process at which such additional plating will not produce anadverse effect. The invention includes the possibility that the platingwill produce not only the cross-conductor but also at least part of thelaminar conductive members in the device.

[0097] The plating techniques which are used for making conductive viasthrough insulating circuit boards can be used in the present invention.However, in this invention the plating serves merely to convey currentacross the device, whereas a plated via must make good electricalcontact with another component. Consequently, the plating qualityrequired in this invention may be less than that required for a via.

[0098] Another technique for providing the cross-conductors is to placea moldable or liquid conductive composition in preformed apertures, andif desired or necessary to treat the composition, while it is in theapertures, so as to produce cross-conductors of desired properties. Thecomposition can be supplied selectively to the apertures, e.g. by meansof a screen, or to the whole assembly, if desired after pretreating atleast some of the assembly so that the composition does not stick to it.For example, a molten conductive composition, e.g. solder, could be usedin this way, if desired using wave soldering techniques; and aperturesin a PTC ceramic element could be filled with a conductive ceramic pastewhich was fired or otherwise consolidated in situ.

[0099] The cross-conductor can also be provided by a preformed member,e.g. a metal rod or tube, for example a rivet. When such a preformedmember is used, it can create the aperture as it is put in place in thedevice.

[0100] The cross-conductor can partially or completely fill theaperture. When the aperture is partially filled, it can be furtherfilled (including completely filled) during the process in which thedevice is connected to other electrical components, particularly by asoldering process. This can be encouraged by providing additional solderin and around the aperture, especially by including a plating of solderin and around the aperture. Normally at least a part of thecross-conductor will be put in place before the device is connected toother electrical components. However, the invention includes thepossibility that the cross-conductor is formed during such a connectionprocess, as for example by the capillary action of solder during asoldering process.

[0101] Assemblies

[0102] As briefly noted above, the assemblies of the inventioncontaining cross-conductors include both devices which are ready forconnection to other electrical components and structures which (ifnecessary after further processing) can be divided into a plurality ofelectrical devices.

[0103] In the devices which are ready for connection, the “first laminarconductive member” (to which the cross-conductor is physically andelectrically connected) provides the first electrode, and the devicegenerally also includes a second laminar conductive member which is notconnected to the first electrode or the cross-conductor and whichprovides the second electrode. The first and second electrodes aregenerally secured, directly or indirectly, to opposite faces of alaminar PTC element, and the current-carrying part of the PTC element isthat part which lies between the two electrodes. Preferably the devicealso includes a third laminar conductive member which (a) is secured tothe second face of the PTC element in the area of the aperture, (b) iselectrically connected to the cross-conductor, and (c) is spaced apartfrom the second electrode. Thus this third member provides a conductivepad through which connection can be made to the first electrode (via thecross-conductor) and which is easier to make a connection to than thecross-conductor alone. This third member is preferably a residual memberformed by removing a part of a laminar conductive member, in particularfrom one laminar conductive member of an assembly comprising two laminarconductive members and a PTC element between them; the other part of theconductive member provides the second electrode. The shape of the thirdmember, and of the gap between the third member and the secondelectrode, can be varied to suit the desired characteristics of thedevice and for ease of manufacture. Thus the third member isconveniently a small rectangle at one end of a rectangular device,separated from the second electrode by a rectangular gap, as shown forexample in FIGS. 1 and 2; but other arrangements are possible. Forexample the third member can be an island separated from the secondelectrode by a gap of closed cross section. If two or more devices inparallel are needed there can be two or more second electrodes on thesecond face of the PTC element, with a single first electrode which ison the first face of the PTC element and to which connection is made viathe cross-conductor. When two or more devices in series are required,the third member of one device can be connected to the second electrodeof the adjacent device; the devices can be joined together bynon-current-carrying sections of the PTC conductive polymer element, orotherwise.

[0104] In the simplest devices, there is a single first electrode, asingle cross-conductor, a single third member, and a single secondelectrode. Such a device is illustrated in FIGS. 1 and 2. A disadvantageof such a device is that it must be placed on the circuit board theright way up. This disadvantage can be overcome (at the expense ofadditional material and processing costs) by making a device which hastwo third members (one associated with each electrode) and twocross-conductors (one associated with each third member). Such a deviceis illustrated in FIGS. 5 and 6.

[0105] A particularly preferred embodiment of this invention is acircuit protection device which has a resistance of less than 15 ohm,preferably less than 10 ohm, particularly less than 5 ohm, especiallyless than 1 ohm, and which comprises

[0106] (1) a laminar PTC resistive element which

[0107] (a) is composed of a conductive polymer which has a resistivityat 25° C. of less than 50 ohm-cm, preferably less than 10 ohm-cm,particularly less than 5 ohm-cm, and which exhibits PTC behavior, and

[0108] (b) has a first face and second face;

[0109] (2) a first metal foil electrode which contacts the first face ofthe PTC element;

[0110] (3) a second metal foil electrode which contacts the second faceof the PTC element; and

[0111] (4) an additional metal foil conductive member which contacts thesecond face of the PTC element and is spaced apart from the secondelectrode;

[0112] the PTC element, the first electrode and the additionalconductive member defining an aperture which runs between the firstelectrode and the additional conductive member, through the PTC element;

[0113] and

[0114] (5) a transverse conductive member which

[0115] (a) is composed of metal,

[0116] (b) lies within the aperture, and

[0117] (c) is physically and electrically connected to the firstelectrode and the additional conductive member.

[0118] The devices of the invention which contain cross-conductors andwhich are ready for connection can be of any appropriate size. However,it is an important advantage of this aspect the invention that verysmall devices can be easily prepared. Preferred devices have a maximumdimension of at most 12 mm, preferably at most 7 mm, and/or a surfacearea of at most 30 mm², preferably at most 20 mm², especially at most 15mm².

[0119] In the assemblies of the invention which contain cross-conductorsand which, if necessary after further processing, can be divided into aplurality of devices, preferably

[0120] (a) the PTC resistive element defines a plurality of theapertures running between the first and second faces of the PTC element,

[0121] (b) there are a plurality of the transverse conductive members,each of the transverse members lying within one of the apertures, and

[0122] (c) the apertures and the transverse members are arranged in aregular pattern.

[0123] Generally the assembly further comprises

[0124] (3) a first laminar conductive member which (a) is secured to thefirst face of the PTC element, and (b) is physically and electricallyconnected to all the transverse members; and

[0125] (4) a second laminar conductive member which is secured to thesecond face of the PTC element.

[0126] The transverse members can also be physically and electricallyconnected to a second laminar conductive member. The first and/or secondconductive members, before the assembly is divided and before or afterthe transverse members are put in place, are preferably in the form of aplurality of strips, arranged so that the assembly can be divided, alonglines parallel to the strips, into devices which comprise first andsecond electrodes and a third member which is on the same face of thePTC element as the second electrode but is not connected to the secondelectrode.

[0127] Processes

[0128] The devices of the invention containing cross-conductors can beprepared in any way. However, the preferred methods of the inventionmake it possible to prepare devices very economically by carrying outall or most of the process steps on a large laminate, and then dividingthe laminate into a plurality of individual devices, or into relativelysmall groups of devices which are connected together physically andwhich may be connected to each other electrically, in series or inparallel or both. The division of the laminate can be carried out alonglines which pass through one or both or neither of the laminarconductive members or through none, some or all of the cross-conductors.The process steps prior to division can in general be carried out in anyconvenient sequence. Preferred processes for making the devices aredisclosed in U.S. patent Ser. Nos. 08/242,916 and 08/257,586 (MP1509-US1and MP1515-US1) incorporated by reference herein.

Drawings Illustrating Devices Containing Cross-Conductors

[0129] The invention is illustrated in the accompanying drawings, inwhich the size of the apertures and the thicknesses of the componentshave been exaggerated in the interests of clarity. FIG. 1 is a plan viewof a circuit protection device of the invention, and FIG. 2 is a crosssection on line II-II of FIG. 1. The device includes a laminar PTCelement 17 having a first face to which first laminar electrode 13 isattached and a second face to which second laminar electrode 15 isattached. Also attached to the second face is an additional laminarconductive member 49 which is not electrically connected to electrode15. Cross-conductor 51 lies within an aperture defined by firstelectrode 13, PTC element 17 and additional member 49. Thecross-conductor is a hollow tube formed by a plating process which alsoresults in a plating 52 on the surfaces of the device which were exposedduring the plating process.

[0130]FIGS. 3 and 4 are similar to FIG. 2 but show cross-conductorswhich are in the form of a metal rod (FIG. 3) or a rivet (FIG. 4).

[0131]FIG. 5 is a plan view of another circuit protection device of theinvention which has been soldered to a circuit board, and FIG. 6 is across section on line VI-VI of FIG. 5. The device is similar to thatshown in FIGS. 1 and 2 but has been made symmetrical so that it can beplaced on a circuit board either way up. Thus the device includes asecond cross-conductor 31 which connects the second electrode 15 to asecond additional member 35. The cross-conductors were made by platingthe apertures (and the other exposed surfaces) first with copper andthen with solder. The device has been soldered to traces 41 and 43 on aninsulating substrate 9. During the soldering process the solder platingon the device flows and completely fills the apertures.

[0132]FIG. 7 is a plan view of a part of an assembly of the inventionwhich can be divided into a number of individual devices as shown inFIGS. 1 and 2, and FIG. 8 is a cross section on line VIII-VIII of FIG.7. The assembly includes a laminar PTC element 7 having a first face towhich first laminar conductive member 3 is attached and a second face towhich second laminar conductive member 5 is attached. The conductivemembers 3 and 5 are not continuous but are in the form of parallelstrips formed by removing, e.g. by etching, strips of electrode materialfrom a corresponding continuous member. The material is removed instaggered strips alternately from opposite sides of the assembly, inorder to balance the physical stresses in the product. Before theetching step, a plurality of holes, arranged in a regular pattern, havebeen drilled through the PTC element 7 and the laminar members 3 and 5,and the assembly has then been plated to provide a tubularcross-conductor 1 in each of the apertures (and a plating 2 on otherexposed surfaces of the assembly). The assembly can be converted into aplurality of devices by dividing it along the lines marked C. At theedge of the assembly, there are registration holes 4 for use in locatingthe holes to be drilled through the element 7 and members 3 and 5, andin locating the lines of division C.

EXAMPLE ILLUSTRATING DEVICES CONTAINING CROSS-CONDUCTORS Example 1

[0133] A conductive polymer composition was prepared by pre blending48.6% by weight high density polyethylene (Petrothene™ LB 832, availablefrom USI) with 51.4% by weight carbon black (Raven™ 430, available fromColumbian Chemicals), mixing the blend in a Banbury™ mixer, extrudingthe mixed compound into pellets, and extruding the pellets though a 3.8cm (1.5 inch) extruder to produce a sheet with a thickness of 0.25 mm(0.010 inch). The extruded sheet was cut into 0.31×0.41 meter (12×16inches) pieces and each piece was stacked between two sheets of 0.025 mm(0.001 inch) thick electrodeposited nickel foil (available from Fukuda).The layers were laminated under heat and pressure to form a plaque witha thickness of about 0.25 mm (0.010 inch). Each plaque was irradiated to10 Mrad. Each plaque was used to prepare approximately 7000 devices,each having the configuration shown in FIGS. 1 and 2.

[0134] Holes with a diameter of 0.25 mm (0.010 inch) were drilledthrough the thickness of the plaque in a regular pattern to provide onehole for each device. Each hole was deburred and cleaned. The surface ofboth the nickel foil layers and the conductive polymer surrounding thedrilled hole were sensitized using a palladium/copper solution. A copperlayer approximately 0.076 mm (0.003 inch) thick was electroless platedonto the sensitized surfaces and then a 0.025 mm (0.001 inch) thicklayer of tin-lead solder was electroless plated onto the copper surface.Using the following standard photoresist process, a pattern was etchedonto the plaque. First, a dry film (Mylar™ polyester) resist waslaminated onto both surfaces of the plaque and then exposed toultraviolet light to generate a pattern as shown in FIGS. 7 and 8.Second, a ferric chloride solution was used to chemically etch thepattern. During this step, alternating sections on each side of theplaque were etched away to expose the solder and relieve built-upmechanical stress. Third, the etched plaque was rinsed and the resistwas stripped away.

[0135] The plaque was sheared and diced to produce individualrectangular electrical devices. Each device had dimensions of4.57×3.05×0.51 mm (0.180×0.120×0.020 inch). The through-hole waspositioned approximately 3.81 mm (0.015 inch) from the shorter edge ofthe device. A strip of exposed conductive polymer 0.51×3.05 mm(0.020×0.120 inch) was present 0.38 mm (0.015 inch) from thethrough-hole and 1.02 mm (0.040 inch) from the shorter edge of thedevice. Each device had a resistance of approximately 300 mohm.

DETAILED DESCRIPTION OF THE DEVICES, ASSEMBLIES AND METHODS OF THEINVENTION IN WHICH A CROSS-CONDUCTOR IS NOT NECESSARILY EMPLOYED

[0136] Devices

[0137] In one aspect, referred to herein as Aspect A, the presentinvention provides an electrical device which comprises

[0138] (1) a first laminar electrode;

[0139] (2) a second laminar electrode; and

[0140] (3) a laminar resistive element which exhibits PTC behavior, andwhich has a first face to which the first electrode is secured and anopposite second face to which the second electrode is secured;

[0141] the device comprising

[0142] (a) a main portion which comprises

[0143] (i) a main part of the first electrode,

[0144] (ii) a main part of the second electrode, and

[0145] (iii) a main part of the resistive element;

[0146] and

[0147] (b) a first connection leg which extends away from the mainportion and which comprises

[0148] (i) a first leg part of the first electrode which is integralwith the main part of the first electrode, and

[0149] (ii) a first leg part of the resistive element which is integralwith the main part of the resistive element.

[0150] The first connection leg can also include a first leg part of thesecond electrode which is integral with the main part of the secondelectrode. Preferably, however, the first connection leg includes aresidual part of the second electrode which is not connected to the mainpart of the second electrode and which does not, therefore, play anypart of the electrical operation of the device. alternatively, the firstleg can consist essentially of the first leg part of the first electrodeand the first leg part of the resistive element.

First Embodiment of Aspect A of the Invention

[0151] In this embodiment, the device is designed to be mounted inapertures of a substrate, e.g. a printed circuit board.

[0152] The devices of this embodiment preferably also contain

[0153] (c) a second connection leg which extends away from the mainportion, which is spaced away from the first connection leg, and whichcomprises

[0154] (i) a second leg part of the second electrode which is integralwith the main part of the second electrode, and

[0155] (ii) a second leg part of the resistive element which is integralwith the main part of the resistive element.

[0156] The second leg can include a second leg part of the firstelectrode, but preferably includes only a residual part of the firstelectrode which provides useful physical properties but does not playany part in the electrical operation of the device. Alternatively thesecond leg can consist essentially of the second leg part of the secondelectrode and the second leg part of the resistive element. The mainportion and the first and second connection legs are preferablysubstantially coplanar. However, one or both of the legs (or the soleleg, when there is only one) can be inclined to main portion. Generallyeach of the legs will extend away from the main portion by a distance ofat least 0.15 cm, e.g. 0.15 to 1.0 cm, preferably 0.2 to 0.6 cm.

[0157] The first and second connection legs preferably extend away fromthe main portion in substantially the same direction so that they canboth be mounted on a planar substrate, with the main portion of thedevice extending away from the substrate, preferably at right anglesthereto.

[0158] In these devices, it is preferred that the first connection legcomprises a first distal sub-portion spaced away from the main portionof the device and a first stand-off sub-portion which lies between thefirst distal sub-portion and the main portion, and the second connectionleg comprises a second distal sub-portion spaced away from the mainportion of the device and a second stand-off sub-portion which liesbetween the second distal sub-portion and the main portion, with thedistal and stand-off sub-portions being shaped so that when each of thedistal sub-portions is placed in an aperture of an appropriate size inthe planar substrate, the stand-off sub-portions will not pass throughthe apertures and will prevent contact between the substrate and themain portion of the device. Thus one or (preferably) both of the firstand second connection legs can be wedge-shaped or can include a stepwhich lies at the junction between the distal and stand-offsub-portions.

[0159] When the device is prepared merely by cutting it out from auniform laminate of the electrode materials and the resistive material,the device will be one in which (a) the first leg part of the firstelectrode, the first leg part of the resistive element, and a first legpart of the second electrode arm substantially coextensive, and (b) asecond leg part of the first electrode, the second leg part of theresistive element, and the second leg part of the second electrode aresubstantially coextensive.

[0160] In some cases, however, it is preferred that the device should beone in which the first stand-off sub-portion comprises a first bridgesub-portion which extends across the width of the first connection legand which does not include any part of the second electrode; and thesecond stand-off sub-portion comprises a second bridge sub-portion whichextends across the width of the second connection leg and does notinclude any part of the first electrode. Such a device can be preparedby removing a portion of the second electrode from the first connectionleg and by removing a portion of the first electrode from the secondelectrode leg, to give a device in which the first distal sub-portioncomprises a second residual conductive member which, in the absence ofthe first bridge sub-portion, would be integral with the main part ofthe second electrode; and the second distal sub-portion comprises afirst residual conductive member which, in the absence of the secondbridge sub-portion, would be integral with the main part of the firstelectrode. In a device prepared in this way, the second residualconductive member is preferably separated from the second electrode by adistance which is at least as great as the minimum distance between thefirst and second electrodes at any location on the device, e.g. 1.5 to 4times that distance, and the first residual conductive member ispreferably separated from the first electrode by a distance which is atleast as great as the minimum distance between the first and secondelectrodes at any location on the device, e.g. 1.5 to 4 times thatdistance. The portion of the electrode which is removed can have asimple shape, e.g. a rectangular strip, or a more complex shape. We havefound that the physical strength of the leg can be improved by removinga more complex shape, e.g. a V-shaped portion, of the electrode.

[0161] Such a device can also be prepared by removing all of the secondelectrode from the first connection leg and all of the first electrodefrom the second connection leg, or by using corresponding preshapedelectrodes, in which case the first connection leg is free from anyconductive member which, in the absence of the first bridge sub-portion,would be integral with the main part of the second electrode; and thesecond connection leg is free from any conductive member which, in theabsence of the second bridge sub-portion, would be integral with themain part of the first electrode.

Second Embodiment of Aspect A of the Invention

[0162] In this embodiment, the device is designed to be mounted parallelto, preferably spaced apart by a small distance from, a substrate, e.g.a printed circuit board.

[0163] In the devices of this embodiment, the first connection legcomprises

[0164] (i) a first distal sub-portion which

[0165] (a) is spaced away from the main portion of the device,

[0166] (b) comprises a first distal sub-part of the first leg part ofthe first electrode, and

[0167] (c) comprises a first electrical connector which contacts thefirst distal sub-part of the first electrode and extends at least to thesecond face of the laminar resistive element;

[0168] and

[0169] (ii) a first bridge sub-portion which

[0170] (a) lies between the first distal sub-portion and the mainportion of the device,

[0171] (b) extends across the width of the first connection leg, and

[0172] (c) does not include any part of the second electrode;

[0173] whereby the device can be placed flat on a planar insulatingsubstrate having first and second appropriately spaced-apart metalconductors on the surface thereof, with the first electrical connectoradjacent the first m conductor; and electrical connection can be made(a) between the first metal conductor and the first electrode, throughthe first electrical connector, and (b) between the second conductor andthe second electrode.

[0174] Such a device can be made by removing a strip of the secondelectrode from the first connection leg, to give a device in which thefirst distal sub-portion comprises a second residual conductive memberwhich is on the second face of the first leg part of the resistiveelement and which, in the absence of the first bridge sub-portion, wouldbe integral with the main part of the second electrode.

[0175] The first electrical connector is preferably a cross-conductor asdescribed in detail above. However, it can be of any kind, for example aconnector which will remain in place even if it is not bonded to theother parts of the device, for example a U-shaped member which extendsaround the end of the first leg portion and the first electrode and, ifpresent, the second residual conductive member. The connector can beresilient so that it clamps to the remainder of the device.

[0176] So that the device can be placed either way up on the substrate,and/or so that it has balanced electrical properties, the devicepreferably also contains a second connection leg which extends away fromthe main portion of the device; which is spaced apart from the firstconnection leg; which comprises

[0177] (i) a second leg part of the second electrode which is integralwith the main part of the second electrode, and

[0178] (ii) a second leg part of the resistive element which is integralwith the main part of the resistive element;

[0179] and which comprises

[0180] (iii) a second distal sub-portion which

[0181] (a) is spaced apart from the main portion of the device,

[0182] (b) comprises a second distal sub-part of the second leg part ofthe second electrode, and

[0183] (c) comprises a second electrical connector which contacts thesecond distal sub-part of the second electrode and extends at least tothe first face of the laminar resistive element;

[0184] and

[0185] (iv) a second bridge sub-portion which

[0186] (a) lies between the second distal sub-portion and the mainportion of the device,

[0187] (b) extends across the width of the second connection leg, and

[0188] (c) does not include any part of the first electrode;

[0189] whereby the device can be placed flat on a planar insulatingsubstrate having first and second appropriately spaced apart metalconductors on the surface thereof, with either the first electricalconnector or the second electrical connector adjacent one of the metalconductors, and electrical connection can be made between (a) saidelectrical connector and metal conductor and (b) the other metalconductor and the electrode adjacent to the substrate.

[0190] The preferred characteristics of the second distal and bridgesub-portions and the second connection part are substantially the sameas previously described for the first distal and bridge sub-portions andthe first connector.

[0191] In these devices the contacting surfaces are preferably coatedwith solder or tin, or otherwise treated, so that they can all besoldered together in a single step by exposing them to heat.

[0192] Assemblies

[0193] Aspect B

[0194] In another aspect, referred to herein as Aspect B, the inventionprovides an electrical assembly which comprises

[0195] (A) an insulating substrate having a first aperture therein;

[0196] (B) a first metal conductor secured to the insulating substrateand leading to the first aperture; and

[0197] (C) an electrical device which comprises

[0198] (1) a first laminar electrode;

[0199] (2) a second laminar electrode; and

[0200] (3) a laminar resistive element which exhibits PTC behavior andwhich has a first face to which the first electrode is secured and anopposite second face to which the second electrode is secured;

[0201] the device comprising

[0202] (a) a main portion which comprises

[0203] (i) a main part of the first electrode,

[0204] (ii) a main part of the second electrode, and

[0205] (iii) a main part of the resistive element;

[0206] and

[0207] (b) a first connection leg

[0208] which extends away from the main portion,

[0209] which comprises

[0210] (i) a first leg part of the first electrode which is integralwith the main part of the first electrode, and

[0211] (ii) a first leg part of the resistive element which is integralwith the main part of the resistive element, and

[0212] which has a first distal sub-portion spaced away from the mainportion of the device and a first stand-off sub-portion between thefirst distal sub-portion and the main portion;

[0213] the first distal sub-portion including a first distal sub-part ofthe first electrode and lying within the first aperture of thesubstrate;

[0214] the first stand-off sub-portion lying between the substrate andthe main portion of the device;

[0215] the first metal conductor being physically and electricallyconnected to the first distal subpart of the first electrode; and

[0216] all of the electrical current between the first metal conductorand the second electrode of the device passing though the firstelectrode and the resistive element.

[0217] Preferably the insulating substrate has a second aperturetherein; a second metal conductor is secured to the insulating substrateand leads to the second aperture; and the device also contains a secondconnection leg which

[0218] (a) extends away from the main portion,

[0219] (b) is spaced away from the first connection leg,

[0220] (c) comprises

[0221] (i) a second leg part of the second electrode which is integralwith the main part of the second electrode, and

[0222] (ii) a second leg part of the resistive element which is integralwith the main part of the resistive element, and

[0223] (d) has a second distal sub-portion spaced away from the mainportion of the device and a second stand-off sub-portion between thesecond distal sub-portion and the main portion;

[0224] the second distal sub-portion including a second distal sub-partof the second electrode and lying within the second aperture of thesubstrate;

[0225] the second metal conductor being physically and electricallyconnected to the second distal sub-part of the second electrode; and

[0226] all of the electrical current between the second metal conductorand the first electrode of the device passing through the secondelectrode and the resistive element.

[0227] In one preferred assembly, the first leg part of the firstelectrode, the first leg part of the resistive element, and the firstleg part of the second electrode are substantially coextensive; thesecond leg part of the first electrode, the second leg part of theresistive element, and the second leg part of the second electrode aresubstantially coextensive; the first conductor terminates on one side ofthe first aperture and is connected by a first solder joint to the firstleg part of the first electrode, with the distance between any part ofthe first solder joint and the second electrode being at least as greatas the minimum distance between the first and second electrodes at anylocation on the device, e.g. 1.5 to 4 times that distance; and thesecond conductor terminates on one side of the second aperture and isconnected by a second solder joint to the second leg part of the secondelectrode, with the distance between any part of the second solder jointand the first electrode being at least as great as the minimum distancebetween the first and second electrodes at any location on the device,e.g. 1.5 to 4 times that distance.

[0228] In another preferred assembly

[0229] (a) the first stand-off sub-portion comprises a first bridgesub-portion which extends across the width of the first connection legand which does not include any part of the second electrode

[0230] (b) the second stand-off sub-portion comprises a second bridgesub-portion which extends across the width of the second connection legand does not include any part of the first electrode;

[0231] (c) the first distal sub-portion comprises a second residualconductive member which, in the absence of the first bridge sub-portion,would be integral with the main part of the second electrode;

[0232] (d) the second distal sub-portion comprises a first residualconductive member which, in the absence of the second bridgesub-portion, would be integral with the main part of the firstelectrode; and

[0233] (e) the first conductor is connected by a first solder joint tothe first leg part of the first electrode, with the distance between anypart of the first solder joint and the second electrode being at leastas great as the minimum distance between the first and second electrodesat any location on the device; and the second conductor is connected bya second solder joint to the second leg part of the second electrode,with the distance between any part of the second solder joint and thefirst electrode being at least as great as the minimum distance betweenthe first and second electrodes at any location on the device.

[0234] Aspect C

[0235] In another aspect, referred to herein as Aspect C, the inventionprovides an electrical assembly which comprises

[0236] (A) a planar insulating substrate;

[0237] (B) a first metal conductor secured to the insulating substrate;

[0238] (C) a second metal conductor secured to the insulating substrate;and

[0239] (D) an electrical device which comprises

[0240] (1) a first laminar electrode;

[0241] (2) a second laminar electrode; and

[0242] (3) a laminar resistive element which exhibits PTC behavior andwhich has a first face to which the first electrode is secured and anopposite second face to which the second electrode is secured;

[0243] the device comprising

[0244] (a) a main portion which comprises

[0245] (i) a main part of the first electrode,

[0246] (ii) a main part of the second electrode, and

[0247] (iii) a main part of the resistive element;

[0248] and

[0249] (b) a first connection leg

[0250] which extends away from the main portion,

[0251] which comprises

[0252] (i) a first leg part of the first electrode which is integralwith the main part of the first electrode,

[0253] (ii) a first leg part of the resistive element which is integralwith the main part of the resistive element,

[0254] (iii) a first distal sub-portion which

[0255] is spaced away from the main portion of the device,

[0256] comprises a first distal sub-part of the first leg part of thefirst electrode, and

[0257] comprises a first electrical connector which contacts the firstdistal sub-part of the first electrode and extends beyond the secondface of the laminar resistive element;

[0258] and

[0259] (iv) a first bridge sub-portion which

[0260] lies between the fir distal sub-portion and the main portion ofthe device,

[0261] extends across the width of the first connection leg, and

[0262] does not include any part of the second electrode;

[0263] the device being placed generally parallel to the planarinsulating substrate with the second electrode being closer to thesubstrate than the first electrode, the first electrical connector beingconnected to the first metal conductor, and the second electricalconductor being connected to the second electrode.

[0264] In such an assembly, the device preferably also contains a secondconnection leg which extends away from the main portion of the device;which is spaced apart from the first connection leg; which comprises

[0265] (i) a second leg part of the second electrode which is integralwith the main part of the second electrode, and

[0266] (ii) a second leg part of the resistive element which is integralwith the main part of the resistive element;

[0267] and which comprises

[0268] (i) a second distal sub-portion which

[0269] (a) is spaced apart from the main portion of the device,

[0270] (b) comprises a second distal sub-part of the second leg part ofthe second electrode, and

[0271] (c) comprises a second electrical connector which contacts thesecond distal sub-part of the second electrode and extends beyond thefirst face of the laminar resistive element;

[0272] and

[0273] (ii) a second bridge sub-portion which

[0274] (a) lies between the second distal sub-portion and the mainportion of the device,

[0275] (b) extends across the width of the second connection leg, and

[0276] (c) does not include any part of the first electrode.

[0277] Preferably there is a solder joint between each of

[0278] (a) the first electrical connector and the first electrode,

[0279] (b) the first electrical connector and the first metal conductor,and

[0280] (c) the second electrode and the second metal conductor, orbetween the second electrode and an intermediate connector and betweenthe in at connector and the second metal conductor, the intermediateconnector lying between the second electrode and the second metalconductor.

Drawings Illustrating Devices which do not Contain Cross-conductors

[0281]FIG. 9 shows an electrical assembly 1 of the invention and FIG. 10shows a cross-section of electrical assembly 1 along line 2-2 of FIG. 9.In both FIGS. 9 and 10, an electrical device 3 of the invention ismounted into first aperture 5 and second aperture 7 on an insulatingplanar substrate 9, e.g. a circuit board. The section of electricaldevice 3 above line A-A is the main portion 11, in which the main partof the first laminar electrode 13 and the main part of the secondlaminar electrode 15, shown in these Figures as metal foil electrodes,are attached to the main part of the laminar resistive element 17, herea conductive polymer which exhibits PTC behavior. Device 3 comprises twoconnection legs 19 and 27 which are coplanar and extend away from mainportion 11 and are used to insert device 3 into the substrate 9. Firstconnection leg 19 comprises a first leg part of the first electrode anda first leg part of the resistive element. In addition, first connectionleg 19 comprises a first distal sub-portion 21, a first stand-offsub-portion, shown here in the form of a step, and a first bridgesub-portion 25 (on the back surface of FIG. 1). Second connection leg 27comprises a second stand-off sub-portion 29, second distal sub-portion31 which lies at least partly within the second aperture 7, and secondbridge sub-portion 33. Second distal sub-portion 31 includes the seconddistal subpart of the second electrode and lies within the secondaperture 7 of the substrate. As shown in FIG. 10, below line A-A lie afirst residual conductive member which is part of the second connectionleg 27, as well as the second leg part of the second electrode 37 andthe second leg part of the resistive element 39. In order to makeelectrical contact to the electrical device 3, connection is madebetween the electrical device 3 and the first metal conductor 41, aconductive trace which leads to the first aperture and is secured to thesubstrate, and between the electrical device 3 and the second metalconductor 43 which leads to the second aperture and is secured to thesubstrate. As shown in FIG. 10, solder 45 is used to make connectionbetween second metal conductor 43 and the second laminar electrode 15,as well as between the second metal conductor 43 and the residual partof the electrode 13.

[0282]FIG. 11 shows a plan view of another electrical assembly 1 of theinvention, FIG. 12 shows a cross-section of electrical assembly 1 alongline 4-4 of FIG. 11, and FIG. 13 is a bottom view of the assembly ofFIG. 11 along line 5-5 before and after insertion and electricalconnection of a device of the invention. As shown in FIGS. 9 and 10,electrical device 3 is inserted onto insulating planar substrate 9through first aperture 5 and second aperture 7 by means of firstconnection leg 19 and second connection leg 27, respectively. For thisdevice, the first connection leg 19 and the second connection leg 27 arein the form of wedges, an neither a first bridge sub-portion nor asecond bridge-sub-portion is present. In FIG. 12, the second distalsub-portion 31 of the second connection leg 27 is visible, and, belowline A-A, the second leg part of the first electrode 37 and the secondleg part of the resistive element 39 are shown. First metal conductor 41leads to and terminates on one side of first aperture 5, and second metconductor 43 leads to and terminates on the opposite side of secondaperture 7. As shown in FIG. 12, electrical connection is made betweenthe first laminar electrode 13 and the first metal conductor 43 by meansof solder joint 47.

[0283]FIG. 14 is a top view of another assembly 1 of the invention andFIG. 15 is a cross-sectional view through the thickness of the assembly1 in which the electrical device 3 is suitable for installing as asurface mounted device. In this assembly, the electrical device 3comprises a laminar resistive element 61 which is laminated to the mainportion of the first electrode 13 and the first residual conductivemember 35 and to the main portion of the second electrode 15 and thesecond residual conductive member 49. (The main portion 11 of the devicelies between lines C and D.) Attached to first connection leg 19 aroundfirst distal sub-portion 21 is U-shaped first connector 51. Attached tosecond connection leg 27 around second distal sub-portion 31 is U-shapedsecond connector 53. A solder joint 59 lies between the periphery of thefirst connector 51 and the first electrode 13 and between the peripheryof the second connector 53 and the second electrode 15. First bridgesub-portion 25 lies between lines D and E and second bridge sub-portion33 lies between lines B and C. Electrical connection is made from thefirst connector 51 to a first metal conductor 41 secured to insulatingsubstrate 9 by means of first solder joint 55, and from the secondconnector 53 to second metal connector 43 secured to the insulatingsubstrate 9 by means of second solder joint 57.

EXAMPLES ILLUSTRATING DEVICES WHICH DO NOT CONTAIN CROSS-CONDUCTORSExample 2

[0284] A conductive polymer composition was prepared by pre blending48.6% by weight high density polyethylene (Petrothene LB832, availablefrom USI) with 51.4% by weight carbon black (Raven 430, available fromColumbian chemicals). The blend was mixed in a Banbury mixer, and theresulting composition was extruded through a 63.5 mm (2.5 inch) extruderto form a sheet with a thickness of 0.51 mm (0.020 inch). Two sheets ofextrudate were laminated together to give a sheet with a thickness ofabout 1 mm (0.040 inch). The sheet was on each side with 0.025 mm (0.001inch) thick electrodeposited nickel foil (available from Fukuda) and thelaminate was irradiated to a dose of 10 Mrad using a 4.5 MeV electronbeam. An electrical device with a shape as shown in FIG. 1 was cut fromthe irradiated sheet. The main portion had a width of approximately 7.75mm (0.305 inch) and a length of approximately 19.7 mm (0.775 inch). Thefirst connection leg and the second connection leg each had a length of5.25 mm (0.207 inch). There was a maxim distance between the first andsecond connection legs at the first and second distal sub-portions of3.8 mm (0.150) inch, and a distance between the step of the firststandoff sub-portion and the step of the second standoff sub-portion of2.0 mm (0.080 inch). The length of the first bridge sub-portion on thefirst connection leg and of the second bridge sub-portion on the secondconnection leg was 1.27 mm (0.05 inch). The first and second bridgesub-portions were created by scoring the nickel foil and peeling itcompletely away from the conductive polymer resistive element.

[0285] The first and second connection legs of the electrical devicewere inserted into first and second apertures, respectively, of aprinted circuit board to form an assembly. The assembly was thenwave-soldered, causing the electrical traces on the circuit boardleading to the first and second apertures to be connected by solder tothe first and second connection legs, respectively, as shown in FIG. 10.Solder completely surrounded the first and second connection legs.

Example 3

[0286] A conductive polymer composition was mixed, extruded, laminated,and irradiated as in Example 2. An electrical device with a shape asshown in FIG. 11 was cut from the irradiated sheet. The main portion hada width of approximately 7.8 mm (0.307 inch) and a length of 21 mm(0.827 inch). The first and second leg portions each had a length of 4mm is (0.157 inch) and tapered from a maximum of 2.5 mm (0.098 inch) atthe junction with the main portion to a minimum of 1.75 mm (0.068 inch)at the first distal sub-portion and the second distal sub-portion. Nobridge sub-portions were created.

[0287] The first and second connection legs of the electrical devicewere inserted into first and second apertures, as in Example 2. In thiscase, however, the electrical traces on the circuit board made contactwith only one of the electrodes. Thus when the assembly was subjected towave soldering, only one side of the device was electrically connectedto each of the traces, as shown in FIGS. 12 and 13.

We claim:
 1. An electrical device which comprises (1) a first laminarelectrode; (2) a second laminar electrode; and (3) a laminar resistiveelement which exhibits PTC behavior, and which has a first face to whichthe first electrode is secured and an opposite second face to which thesecond electrode is secured; the device comprising (a) a main portionwhich comprises (i) a main part of the first electrode, (ii) a main partof the second electrode, and (iii) a main part of the resistive element;and (b) a first connection leg which extends away from the main portionand which comprises (i) a first leg part of the first electrode which isintegral with the main part of the first electrode, and (ii) a first legpart of the resistive element which is integral with the main part ofthe resistive element.
 2. A device according to claim 1 which alsocontains (c) a second connection leg which extends away from the mainportion, which is spaced away from the first connection leg, and whichcomprises (i) a second leg part of the second electrode which isintegral with the main part of the second electrode, and (ii) a secondleg part of the resistive element which is integral with the main partof the resistive element.
 3. A device according to claim 2 wherein themain portion and the first and second connection legs are substantiallycoplanar; the first and second connection legs extend away from the mainportion in substantially the same direction so that they can both bemounted on a planar substrate with the main portion of the deviceextending away from the substrate; the first connection leg comprises afirst distal sub-portion spaced away from the main portion of the deviceand a first stand-off sub-portion which lies between the first distalsub-portion and the main portion, and the second connection legcomprises a second distal sub-portion space away from the main portionof the device and a second stand-off sub-portion which lies between thesecond distal sub-portion and the main portion, the distal and stand-offsub-portions being shaped so that when each of the distal sub-portionsis placed in an aperture of an appropriate size in the planar substrate,the stand-off sub-portions will not pass through the apertures and willprevent contact between the substrate and the main portion of thedevice.
 4. A device according to claim 3 wherein each of the first andsecond connection legs is wedge-shaped or includes a step which lies atthe junction between the distal and stand-off sub-portions.
 5. A deviceaccording to claim 2 wherein the first connection leg contains a firstleg part of the second electrode which is integral with the main part ofthe second electrode; the second connection leg contains a second legpart of the first electrode which is integral with the main part of thefirst electrode; the first leg part of the first electrode, the firstleg part of the resistive element, and a first leg part of the secondelectrode are substantially coextensive; and a second leg part of thefirst electrode, the second leg part of the resistive element, and thesecond leg part of the second electrode are substantially coextensive.6. A device according to claim 3 wherein the first stand-off sub-portioncomprises a first bridge sub-portion which extends across the width ofthe first connection leg and which does not include any part of thesecond electrode; and the second stand-off sub-portion comprises asecond bridge sub-portion which extends across the width of the secondconnection leg and does not include any part of the first electrode. 7.A device according to claim 6 wherein the first distal sub-portioncomprises a second residual conductive member which, in the absence ofthe first bridge sub-portion, would be integral with the main part ofthe second electrode; the second distal sub-portion comprises a firstresidual conductive member which, in the absence of the second bridgesub-portion, would be integral with the main part of the firstelectrode; the second residual conductive member is separated from thesecond electrode by a distance which is at least as great as the minimumdistance between the first and second electrodes at any location on thedevice; and the first residual conductive member is separated from thefirst electrode by a distance which is at least as great as the minimumdistance between the first and second electrodes at any location on thedevice.
 8. A device according to claim 2 wherein the laminar resistiveelement is composed of conductive polymer and each of the electrodes isa metal foil.
 9. A device according to claim 8 which has a resistance at23° C. of less than 50 ohm.
 10. A device according to claim 1 whereinthe laminar resistive element is composed of conductive polymer, each ofthe electrodes is a metal foil, and the first connection leg comprises(i) a first distal sub-portion which (a) is spaced away from the mainportion of the device, (b) comprises a first distal sub-part of thefirst leg part of the first electrode, and (c) comprises a firstelectrical connector which contacts the first distal sub-part of thefirst electrode and extends at least to the second face of the laminarresistive element; and (ii) a first bridge sub-portion which (a) liesbetween the first distal sub-portion and the main portion of the device,(b) extends across the width of the first connection leg, and (c) doesnot include any part of the second electrode; whereby the device can beplaced flat on a planar insulating substrate having first and secondappropriately spaced-apart metal conductors on the surface thereof, withthe first electrical connector against the first metal conductor, andelectrical connection can be made (a) between the first metal conductorand the first electrode, through the first electrical connector, and (b)between the second conductor and the second electrode.
 11. A deviceaccording to claim 10 wherein the first distal sub-portion comprises asecond residual conductive member which is on the second face of thefirst leg part of the resistive element and which, in the absence of thefirst bridge sub-portion, would be integral with the main part of thesecond electrode, and the first electrical connector is a U-shapedmember which extends around the end of the first leg portion andcontacts the first electrode and the second residual conductive member.12. A device according to claim 10 which also contains a secondconnection leg which extends away from the main portion of the device;which is spaced apart from the first connection leg; which comprises (i)a second leg part of the second electrode which is integral with themain part of the second electrode, and (ii) a second leg part of theresistive element which is integral with the main part of the resistiveelement; and which comprises (i) a second distal sub-portion which (a)is spaced apart from the main portion of the device, (b) comprises asecond distal sub-part of the second leg part of the second electrode,and (c) comprises a second electrical connector which contact the seconddistal sub-part of the second electrode and extends at least to thefirst face of the laminar resistive element; and (ii) a second bridgesub-portion which (a) lies between the second distal sub-portion and themain portion of the device, (b) extends across the width of the secondconnection leg, and (c) does not include any part of the firstelectrode; whereby the device can be placed flat on a planar insulatingsubstrate having first and second appropriately spaced apart metalconductors on the surface thereof, with either the first electricalconnector or the second electrical connector against one of the metalconductors, and electrical connection can be made between (a) saidelectrical connector and metal conductor and (b) the other metalconductor and the electrode adjacent to the substrate.
 13. A deviceaccording to claim 12 wherein the first distal sub-portion comprises asecond residual conductive member which is on the second face of thefirst leg part of the resistive element and which, in the absence of thefirst bridge sub-portion, would be integral with the main part of thesecond electrode, the second distal sub-portion comprises a firstresidual conductive member which is on the first face of the second legpart of the resistive element and which, in the absence of the secondbridge sub-portion, would be integral with the main part of the firstelectrode; the first electrical connector is a U-shaped member whichextends around the end of the first leg portion and contacts the firstelectrode and the second residual conductive member; and the secondelectrical connector is a U-shaped member which extends around the endof the second leg portion and contacts the second electrode and thefirst residual conducive member.
 14. A device according to claim 13wherein the contacting surfaces of the first electrical connector, thefirst electrode and the second residual conductive member are such thatthese contacting sure can be soldered together by exposing them to heat;and the contacting surfaces of the second electrical connector, thesecond electrode and the first residual conductive member are such thatthese contacting surfaces can be soldered together by exposing them toheat.
 15. A method of making an electrical device which comprises (1) afirst laminar electrode; (2) a second laminar electrode; and (3) alaminar resistive element which exhibits PTC behavior has a first faceto which the first electrode is secured and an opposite second face towhich the second electrode is secured; the device comprising (a) a mainportion which comprises (i) a main part of the first electrode, (ii) amain part of the second electrode, and (iii) a main part of theresistive element; (b) a first connection leg which extends away fromthe main portion and which comprises (i) a first leg part of the firstelectrode which is integral with the main part of the first electrode,and (ii) a first leg part of the resistive element which is integralwith the main part of the resistive element; and (c) a second connectionleg which extends away from the main portion, which is spaced away fromthe first connection leg, and which comprises (i) a second leg part ofthe second electrode which is integral with the main part of the secondelectrode, and (ii) a second leg part of the resistive element which isintegral with the main part of the resistive element; which methodcomprises (A) providing a planar laminate which comprises (1) a firstlaminar metal member; (2) a second laminar metal member, and; (3) alaminar resistive member which (i) lies between the first and secondmembers, (ii) exhibits PTC behavior, and (iii) is composed of conductivepolymer; and (B) cutting a plurality of said electrical devices from theplanar laminate.
 16. An electrical assembly which comprises (A) aninsulating substrate having a first aperture therein; (B) a first metalconductor secured to the insulating substrate and leading to the firstaperture; and (C) an electrical device which comprises (1) a firstlaminar electrode; (2) a second laminar electrode; and (3) a laminarresistive element which exhibits PTC behavior and which has a first faceto which the first electrode is secured and an opposite second face towhich the second electrode is secured; the device comprising (a) a mainportion which comprises (i) a main part of the first electrode, (ii) amain part of the second electrode, and (iii) a main part of theresistive element; and (b) a first connection leg which extends awayfrom the main portion, which comprises (i) a first leg part of the firstelectrode which is integral with the main part of the first electrode,and (ii) a first leg part of the resistive element which is integralwith the main part of the resistive element, and which has a firstdistal sub-portion spaced away from the main portion of the device and afirst stand-off sub-portion between the first distal sub-portion and themain portion; the first distal sub-portion including a first distalsub-part of the first electrode and lying within the first aperture ofthe substrate; the first stand-off sub-portion lying between thesubstrate and the main portion of the device; the first metal conductorbeing physically and electrically connected to the first distal sub-partof the first electrode; and all of the electrical current between thefirst metal conductor and the second electrode of the device passingthrough the first electrode and the resistive element.
 17. An assemblyaccording to claim 16 wherein the insulating substrate has a secondaperture therein; wherein a second metal conductor is secured to theinsulating substrate and leads to the second aperture; and wherein thedevice also contains a second connection leg which (a) extends away fromthe main portion, (b) is spaced away from the first connection leg, (c)comprises (i) a second leg part of the second electrode which isintegral with the main part of the second electrode, and (ii) a secondleg part of the resistive element which is integral with the main partof the resistive element, and (d) which has a second distal sub-portionspaced away from the main portion of the device and a second stand-offsub-portion between the second distal sub-portion and the main portion;the second distal sub-portion including a second distal sub-part of thesecond electrode and lying within the second aperture of the substrate;the second metal conductor being physically and electrically connectedto the second distal sub-part of the second electrode; and all of theelectrical current between the second metal conductor and the firstelectrode of the device passing through the second electrode and theresistive element.
 18. An electrical assembly which comprises (A) aplanar insulating substrate; (B) a first metal conductor secured to theinsulating substrate; (C) a second metal conductor secured to theinsulating substrate; and (D) an electrical device which comprises (1) afirst metal foil electrode; (2) a second metal foil electrode; and (3) alaminar resistive element which exhibits PTC behavior, which is composedof conductive polymer, and which has a first face to which the firstelectrode is secured and an opposite second face to which the secondelectrode is secured; the device comprising (a) a main portion whichcomprises (i) a main part of the first electrode, (ii) a main part ofthe second electrode, and (iii) a main part of the resistive element;and (b) a first connection leg which extends away from the main portion,which comprises (i) a first leg part of the first electrode which isintegral with the main part of the first electrode, (ii) a first legpart of the resistive element which is integral with the main part ofthe resistive element, (iii) a first distal sub-portion which is spacedaway from the main portion of the device, comprises a first distalsub-part of the first leg part of the first electrode, and comprises afirst electrical connector which contacts the first distal sub-part ofthe first electrode and extends beyond the second face of the laminarresistive element; and (iv) a first bridge sub-portion which liesbetween the first distal sub-portion and the main portion of the device,extends across the width of the first connection leg, and does notinclude any part of the second electrode; the device being placedgenerally parallel to the planar insulating substrate with the secondelectrode being closer to the substrate than the first electrode, thefirst electrical connector being connected to the first metal conductor;and the second conductor being connected to the second electrode.
 19. Anassembly according to claim 18 wherein the device also contains a secondconnection leg which extends away from the main portion of the device;which is spaced apart from the first connection leg; which comprises (i)a second leg part of the second electrode which is integral with themain part of the second electrode, and (ii) a second leg part of theresistive element which is integral with the main part of the resistiveelement; and which comprises (i) a second distal sub-portion which (a)is spaced apart from the main portion of the device, (b) comprises asecond distal sub-part of the second leg part of the second electrode,and (c) comprises a second electrical connector which contacts thesecond distal sub-part of the second electrode and extends beyond thefirst face of the laminar resistive element; and (ii) a second bridgesub-portion which (a) lies between the second distal sub-portion and themain portion of the device, (b) extends across the width of the secondconnection leg, and (c) does not include any part of the firstelectrode; and wherein the second conductor is connected to the secondelectrode through the second connector.
 20. An assembly according toclaim 18 wherein there is a solder joint between each of (a) the firstelectrical connector and the first electrode, (b) the first electricalconnector and the first metal conductor, and (c) the second electrodeand the second metal conductor, or between the second electrode and anintermediate connector which lies between the second electrode and thesecond metal conductor, and between the intermediate connector and thesecond metal conductor.
 21. An assembly which comprises (1) a PTCresistive element which (a) is composed of a resistive material whichexhibits PTC behavior, (b) has a first face and a second face, and (c)defines an aperture which runs between the first and second faces; (2) atransverse conductive member which (a) lies within the aperture definedby the PTC element, (b) runs between the first and second faces of thePTC element, and (c) is secured to the PTC element; and (3) a firstlaminar conductive member which (a) is secured to the first face of thePTC element and (b) is physically and electrically connected to thetransverse conductive member.
 22. A circuit protection device which hasa resistance of less than 15 ohm and which comprises (1) a laminar PTCresistive element which (a) is composed of a conductive polymer whichhas a resistivity at 25° C. of less than 50 ohm-cm and which exhibitsPTC behavior, and (b) has a fit face and second face; (2) a first metalfoil electrode which contacts the first face of the PTC element; (3) asecond metal foil electrode which contacts the second face of the PTCelement; and (4) an additional metal foil conductive member whichcontacts the second face of the PTC element and is spaced apart from thesecond electrode; the PTC element, the first electrode and theadditional conductive member defining an aperture which runs between thefirst electrode and the additional conductive member, through the PTCelement; and (5) a transverse conductive member which (a) is composed ofmetal, (b) lies within the aperture, and (c) is physically andelectrically connected to the first electrode and the additionalconductive member.
 23. An electrical assembly which comprises (A) aprinted circuit board including first and second conductive traces on asurface thereof, and (B) an electrical device which comprises (1) alaminar FTC resistive element which (a) is composed of a resistivematerial which exhibits PTC behavior, and (b) has a first face and asecond face; (2) a first laminar electrode which is secured to the firstface of the PTC element; (3) a second laminar electrode which is securedto the second face of the PTC element; (4) an additional laminarconductive member which (a) is secured to the second face of the PTCelement and (b) is spaced apart from the second electrode; the PTCelement, the first electrode and the additional laminar conductivemember defining an aperture which runs between the first electrode andthe additional conductive member, through the PTC element; and
 24. Amethod of making an electrical device which comprises (A) providing anassembly which comprises (1) a laminar PTC resistive element which (i)is composed of a resistive material exhibiting PTC behavior, and (ii)has a first face and a second face, (2) a first laminar conductivemember which is secured to the first face of the PTC element, and (3) asecond laminar conductive member which is secured to the second face ofthe PTC element; (B) making a plurality of apertures through thethickness of the assembly provided in step (A), the apertures beingarranged in a regular pattern; (C) simultaneously with step (B), orafter step (B), placing a plurality of transverse conductive memberswithin the apertures, in electrical contact with the first laminarconductive member; (D) removing predetermined portions of at least oneof the first and second conductive members; and (E) after steps (A) to(D), dividing the assembly into a plurality of electrical devices, eachdevice comprising (1) a part of the PTC resistive element, (2) a part ofthe first laminar conductive member, said part providing a firstelectrode in some of the devices and a second electrode in the otherdevices, (3) a part of the second laminar conductive member, said partproviding a second electrode in some of the devices and a firstelectrode in the other devices, (4) a residual part of the secondlaminar conductive member, and (5) at least one transverse conductivemember which electrically connects the residual part and the firstelectrode.
 25. An assembly which comprises (1) a laminar PTC resistiveelement which (i) is composed of a conductive polymer exhibiting PTCbehavior, and (ii) has a first face and a second face, (2) a firstlaminar conductive member which is secured to the first face of the PTCelement, and (3) a second laminar conductive member which is secured tothe second face of the PTC element; the PTC element and the first andsecond laminar conductive members defining a plurality of apertureswhich pass through the thickness of the assembly, and the aperturesbeing arranged in a regular pattern.